Fuel injection systems with air assisted fuel injection to improve fuel atomisation are well known. The gas supply to the injectors has in the past been drawn from a variety of sources. In the simplest form of such systems, ambient air is used to assist atomisation and is drawn into the intake port near to the fuel jet by the manifold vacuum. Such a system can only be used under low load conditions when the intake manifold vacuum is high and is not effective under high engine load conditions.
Other systems have been proposed that use gas from a rail that is pressurised in some manner when the engine is in operation. The rail can be pressurised by an engine driven compressor or by connecting it through one-way valves to the engine combustion chambers. In the latter case, the pressure in the rail may be too high, in which case a regulator is needed to reduce the delivery pressure of the gas to the intake ports.
The disadvantages with such systems is that the rail is permanently under pressure and delivers gas continuously to the intake ports, even at times when it is not required. As drawing gas from the combustion chambers of the engine or using the engine to drive a compressor both take power from the engine, this continuous supply of gas amounts to a waste of energy that increases fuel consumption.
One can use timed ON/OFF valves to limit the supply of gas from the compressed gas rail to the intake ports to the instants when it is required for fuel atomisation, but this increases system complexity and cost.